Issue #3524894: Circular reference error

Closes #3524894

modules/mailer_override/src/MailerConfigOverride.php

@@ -7,7 +7,9 @@ namespace Drupal\mailer_override;
 use Drupal\Core\Cache\CacheableMetadata;
 use Drupal\Core\Config\ConfigFactoryOverrideInterface;
 use Drupal\Core\Config\StorageInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
 
 /**
  * Mailer Override configuration override.
@@ -29,10 +31,15 @@ class MailerConfigOverride implements ConfigFactoryOverrideInterface {
   /**
    * Constructs the MailerConfigOverride object.
    *
+   * @param \Symfony\Component\DependencyInjection\ContainerInterface $container
+   *   The container.
    * @param \Drupal\Core\Extension\ModuleHandlerInterface $moduleHandler
    *   The module handler.
    */
-  public function __construct(protected readonly ModuleHandlerInterface $moduleHandler) {}
+  public function __construct(
+    protected readonly ContainerInterface $container,
+    protected readonly ModuleHandlerInterface $moduleHandler,
+  ) {}
 
   /**
    * {@inheritdoc}
@@ -67,15 +74,13 @@ class MailerConfigOverride implements ConfigFactoryOverrideInterface {
    * Build cache of config overrides.
    */
   protected function buildCache(): void {
-    if (!$this->builtCache && $this->moduleHandler->isLoaded()) {
-      // Getting the definitions can cause reading of config which triggers
-      // `loadOverrides()` to call this function. Protect against an infinite
-      // loop by marking the cache as built before starting.
+    // The calculation of config overrides depends on configuration settings,
+    // so we have to be careful to avoid a circular dependency.
+    // - Wait for key services we depend on to load, as they may read config.
+    // - Avoid dependency injection, instead load services when we use them.
+    // - Mark the cache as built before processing to ensure it only runs once.
+    if (!$this->builtCache && $this->moduleHandler->isLoaded() && $this->container->initialized(EntityTypeManagerInterface::class)) {
       $this->builtCache = TRUE;
-
-      // We cannot use dependency injection because that creates a circular
-      // dependency.
-      /** @var \Drupal\mailer_override\OverrideManagerInterface $overrideManager */
       $overrideManager = \Drupal::service(OverrideManagerInterface::class);
       foreach ($overrideManager->getDefinitions() as $definition) {
         $this->configOverrides = array_merge($this->configOverrides, $definition['config_overrides']);